1. Field of the Invention
The present invention relates to a signal receiving apparatus of the global positioning system and a mobile wireless terminal apparatus, and more particularly, is suitably applied to such as a signal receiving apparatus of the Global Positioning System (GPS) for conducting the location measurement of the mobile unit.
2. Description of the Related Art
Heretofore, in the global positioning system, satellite signals to be transmitted from the plural number of GPS satellites travelling around the earth are received by the GPS receiving apparatus, and by analyzing the received satellite signals, the distance between the GPS signal receiving apparatus and each GPS satellite is obtained. And based on this, the current location of the mobile unit is to be calculated.
The satellite signal to be transmitted from this GPS satellite is the signal spectrum diffused by the pseudo random noise (PN) code formed of code series of different type per each GPS satellite.
Accordingly, the GPS signal receiving apparatus can generate local PN codes corresponding respectively to multiple kinds of GPS satellites, and secures the synchronization by matching the phase of the local PN code generated to the phase of PN code of the satellite signal. And after supplementing the synchronization by tracking the satellite signal, the GPS signal receiving apparatus demodulates the navigation message (such as an orbit information for location measurement) from the GPS satellite by applying the inverse spread spectrum processing and calculates the current location based on the navigation message.
In practice, as shown in FIG. 1, the GPS signal receiving apparatus 1 enters a satellite signal S1 received via a GPS antenna 3 and signal receiving circuit 4 into the correlation circuit 5 of the GPS signal receiving unit 2. The correlation circuit 5, multiplying the local PN code C1 to be supplied from the PN code generation circuit 6 by satellite signal S1, calculates a correlation value S2 and sends this out to the control circuit 7.
When the correlation value S2 is in low level not exceeding the predetermined threshold value, the control circuit 7 judges that the PN code of the satellite signal S1 and the local PN code C1 generated at the PN code generation circuit 6 are not synchronized. And by supplying a phase control signal CTL1 to the PN code generation circuit 6, the control circuit 7 offset controls the phase of the local PN code C1.
The PN code generation circuit 6 offsets the phase of the local PN code C1 based on the phase control signal CTL1, and as well as transmitting the resultant phase-offset local PN code C1 to the correlation circuit 5, this PN code generation circuit 6 sends back the phase result information S3 showing the phase condition of the local PN code C1 to the control circuit 7.
Accordingly, in the case where the control circuit 7 judges that the synchronization has not been secured based on the correlation value S2 from the correlation circuit 5, controlling the PN code generation circuit 6 based on the phase control signal CTL1, it successively offsets the phases of the local PN code C1 by the PN code generation circuit 6 and sends these out.
Furthermore, when the correlation value S2 is at high level more than the predetermined threshold value, the control circuit 7 judges that the PN code of the satellite signal S1 and the local PN code C1 generated at the PN code generation circuit 6 are in synchronism and conducts synchronism supplements.
At this point, the control circuit 7 generates a demodulation control signal S4 for specifying the head timing of the cycle of the PN code obtained by acquiring the synchronization as the demodulation start time of the data synchronized with the PN code and outputs this to the correlation circuit 5.
With this arrangement, the correlation circuit 5 can demodulate the navigation message by applying the spectrum inverse diffusion processing to the satellite signal S1 based on the demodulation control signal S4 inside of the demodulation unit (not shown in Fig.).
In the GPS signal receiving apparatus 1 thus constructed, the PN code of the satellite signal S1 is not synchronized with the local PN code C1 generated at the PN code generation circuit 6 when the correlation value S2 is at the low level lower than the predetermined threshold value. Therefore, it is necessary to sequentially offset phases of the local PN code C1 and repeat the calculation processing of the correlation value S2 by the time the synchronization is obtained by means of the phase control signal CTL1.
In this case, as shown in FIG. 2 in the GPS signal receiving apparatus 1, since the satellite signal S1 is spread spectrum processed by the PN code of 1023 chips, the phase offset for 1023 chips should be conducted at the maximum by the time the synchronism is obtained if the phase relation between the PN code of the satellite signal S1 and the local PN code C1 generated at the PN code generation circuit 6 is not clear.
At this point, in the GPS signal receiving apparatus 1, since it requires a great deal of time to obtain the synchronization, the consumption of electric power is increased, and as a result, it has created a problem that the battery life has become short.
Furthermore, in the GPS signal receiving apparatus 1, in the case of demodulating the navigation message synchronized with the PN code of the satellite signal S1, since the head timing of the cycle of the PN code is not known till the synchronization is secured, it has created a problem that the navigation message could not be obtained unless all satellite signals S1 would be demodulated.
In view of the foregoing, an object of the invention is to provide a signal receiving apparatus of the global positioning system and mobile wireless terminal apparatus capable of securing the synchronization with respect to satellite signals at high speed and reducing the consumption of electric power.
The foregoing object and other objects of the invention have been achieved by the provision of a signal receiving apparatus of the global positioning system and mobile wireless terminal apparatus, in which the transmission signal from the base station of the communications system synchronized with the satellite signal to be transmitted from the satellite of the global positioning system is received, the timing signal as a reference signal used to synchronize with the satellite signal is generated based on the transmission signal of the communication system, the satellite signal is received and the synchronization with the pseudo noise code in the satellite signal is secured based on the timing signal to be supplied from the timing signal generating means, the acquisition of synchronization with the pseudo noise code in the satellite signal can be executed in a short time coinciding with the timing signal. And thus, the consumption of electric power can be further reduced.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.